chore(moonshine): Address remaining PR #259 review nitpicks

This commit addresses the remaining low-priority review comments from PR #259.

Test Improvements:
- Adds `serial_test` to isolate environment variable tests in `moonshine_e2e.rs`.
- Adds a test for `verify_sample_rate()` in `moonshine.rs`.
- Adds a test for buffer overflow protection in `moonshine.rs`.
- Refactors `load_test_audio()` to validate sample rate and channels and removes duplicated test code.

Code Cleanup:
- Removes the unused `active_config` field from `MoonshinePlugin`.

Script Improvements:
- Uses `set -euo pipefail` in `install-moonshine-deps.sh` and `verify-stt-setup.sh`.

Author: google-labs-jules[bot]

.lintstagedrc.json

@@ -11,4 +11,4 @@
   "*": [
     "mise run typos"
   ]
-}
+}

CHANGELOG.md

@@ -5,6 +5,16 @@ All notable changes to this project are documented here.
 ## [Unreleased]
 
 ### Added
+- **Moonshine STT Plugin** - CPU-optimized speech recognition using UsefulSensors' Moonshine model via PyO3/HuggingFace Transformers
+  - 5x faster than Whisper on CPU with comparable accuracy (~2.5% WER)
+  - English-only, optimized for 16kHz audio
+  - Two model variants: Base (61M params, ~500MB) and Tiny (27M params, ~300MB)
+  - Auto-downloads models from HuggingFace Hub on first use
+  - Environment variables: `MOONSHINE_MODEL` (base/tiny), `MOONSHINE_MODEL_PATH`
+  - Requires Python 3.8+ with transformers, torch, librosa
+  - Install deps: `./scripts/install-moonshine-deps.sh`
+  - Build: `cargo build --features moonshine`
+
 - **NVIDIA Parakeet STT Plugin** - GPU-accelerated speech recognition using NVIDIA's Parakeet model via pure-Rust parakeet-rs library (#XXX)
   - Supports largest available model: nvidia/parakeet-tdt-1.1b (1.1 billion parameters)
   - TDT variant: Multilingual support for 25 languages with automatic detection

Cargo.lock

@@ -68,6 +68,7 @@ similar-asserts = "1.5"
 default = ["silero", "text-injection"]
 live-hardware-tests = []
 parakeet = ["coldvox-stt/parakeet"]
+moonshine = ["coldvox-stt/moonshine"]
 whisper = [] # Temporarily stubbed; new pure-Rust backend will populate this
 no-stt = []
 examples = []

crates/app/Cargo.toml

@@ -579,6 +579,13 @@ impl SttPluginManager {
             use coldvox_stt::plugins::parakeet::ParakeetPluginFactory;
             registry.register(Box::new(ParakeetPluginFactory::new()));
         }
+
+        // Register Moonshine plugin if the moonshine feature is enabled
+        #[cfg(feature = "moonshine")]
+        {
+            use coldvox_stt::plugins::moonshine::MoonshinePluginFactory;
+            registry.register(Box::new(MoonshinePluginFactory::new()));
+        }
     }
 
     /// Initialize the plugin manager and select the best available plugin

crates/app/src/stt/plugin_manager.rs

@@ -19,10 +19,20 @@ coldvox-telemetry = { path = "../coldvox-telemetry" }
 # Parakeet STT via pure Rust ONNX Runtime
 parakeet-rs = { version = "0.2", optional = true }
 
+# Moonshine STT via PyO3/HuggingFace
+pyo3 = { version = "0.22", optional = true, features = ["auto-initialize"] }
+tempfile = { version = "3.8", optional = true }
+hound = { version = "3.5", optional = true }
+
+[dev-dependencies]
+anyhow = "1.0"
+serial_test = "3.0.0"
+
 [features]
 default = []
 parakeet = ["dep:parakeet-rs"]
 whisper = [] # Placeholder until new backend is implemented
+moonshine = ["dep:pyo3", "dep:tempfile", "dep:hound"]
 coqui = []
 leopard = []
 silero-stt = []

crates/coldvox-stt/Cargo.toml

@@ -8,6 +8,9 @@ pub mod noop;
 #[cfg(feature = "parakeet")]
 pub mod parakeet;
 
+#[cfg(feature = "moonshine")]
+pub mod moonshine;
+
 #[cfg(feature = "whisper")]
 pub mod whisper_cpp;
 
@@ -27,3 +30,6 @@ pub use noop::NoOpPlugin;
 
 #[cfg(feature = "parakeet")]
 pub use parakeet::ParakeetPluginFactory;
+
+#[cfg(feature = "moonshine")]
+pub use moonshine::{MoonshineModelSize, MoonshinePlugin, MoonshinePluginFactory};